This invention relates to a fuel injection rate control system for an internal combustion engine, such as a diesel engine.
In diesel engines, fuel is periodically injected into engine combustion chambers by means of fuel injection systems. Diesel engines are susceptible to noisy combustion or detonation. This results from ignition lag which causes supply of an excessive quantity of fuel to combustion chambers before ignition begins. To overcome this problem, some conventional fuel injection systems provide pilot fuel charges in advance of main fuel charges. The pilot injection expedites the commencement of ignition of the main charge of fuel, thereby preventing accumulation of an excessive quantity of fuel prior to the commencement of ignition.
In automotive diesel engines, under small engine loads pilot fuel injection and moderate fuel injection rates are actually desirable to prevent noisy combustion and detonation. Under heavy engine loads, pilot fuel injection is unnecessary but high fuel injection rates are necessary in order to achieve adequately high engine power output.
Japanese patent publication No. 57-65857 discloses a fuel injection system providing pilot charges. In this system, pilot fuel injection quantity and rate can be adjusted as a function of engine load. Reductions in the pilot quantity and rate entail concomitant decreases in main fuel injection quantity and rate. Furthermore, it is impossible to completely interrupt the pilot injections in this conventional system. Accordingly, this system does not acceptably meet the injection characteristic requirements described above.